1. Field of the Invention
The present invention generally relates to an optic fiber grating sensor, and more particularly relates to an optic fiber Bragg grating (FBG) sensor applied as a gauge pressure transducer, differential pressure transducer, load cell, and displacement transducer.
2. Description of the Prior Art
Conventionally, most electronic pressure sensors or electronic displacement sensors transform the target physical quantity into strain. The strain is then transformed into a current or voltage signal via various forms of electric resistance or vibrating wire strain gages to facilitate data acquisition.
Meanwhile, most electronic pressure sensors or electronic displacement sensors are of non-distributive design; each sensing unit requires a dedicated signal transmission line. Therefore, the application of such sensors is often limited due to excessive number of transmission lines. Furthermore, the electronic signal can be affected by electromagnetic interference (EMI).
In another aspect, the design principle of the exiting pressure  sensors using optic FBG employs a cantilever beam as a mechanism to transform the sensed pressure into tensile and compressive strains on the opposite sides of the cantilever beam. Thus, the FBG's attached to the two opposite sides of the cantilever beam experience strains of the same value but with opposite signs. The pressure value is determined by subtracting the peak FBG signal from another. In another method, a single FBG is passed through a neutral layer of the cantilever beam to transform the sensed pressure into a chirped strain. The chirped strain caused a change in the width of the FBG waveform, instead of its peak value. In either case, the cantilever beam must be isolated to achieve the hermetic packaging. A separate diaphragm is required to isolate the cantilever beam from the pressure chamber. Such designs are more complex and less sensitive. Other existing optical fiber sensors are not fabricated by using the FBG's, they are non-distributive and carries all the disadvantages of non-distributive sensors.